Seals of the above-mentioned type are earlier known and exist in a very large number of embodiments. They usually are fitted to the non-mobile part and seals against the rotating shaft, or some member fitted thereto, by means of one or more sealing lips which preferably consist of rubber. Seals fitted to the rotating shaft are also known. The common feature of all these seals is that the sealing lip shall be given a proper pressure against another part in the device and thus prevent dirt, water and the like from penetrating into the space intended to be sealed off. It is very important that the lip contacts with a suitable pressure. If this pressure becomes too high the friction will be too big and if it becomes too low, then the sealing function will be poor.
The space outside the seal sometimes can be very fouled, which puts big demands on the seal. In order to obtain a satisfactory sealing effect, there is sometimes provided several seals, often of different types, such as lip seals combined with labyrinth seals. One purpose thereof is that such a low amount of dirt as possible shall come into contact with the final inner seal. Such an arrangement with several seals can be complex and thereby also expensive to manufacture as well as assemble.